In the trial of Mary Queen of Scots, in 1568, incriminating "casket" letters were introduced into evidence against her, to show that she murdered her husband. The long [second] casket letter includes a reference to a "Laird" [the Scottish term for a landholder, especially one who holds land directly of the crown] of Lusse [Lus], Howstoun [Houston], and Caldwellis sone [son]." Can anyone tell me more who this Caldwellis was?